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mnttab(4)

mnttab(4)                        File Formats                        mnttab(4)



NAME
       mnttab - mounted file system table

DESCRIPTION
       The  file  /etc/mnttab  is really a file system that provides read-only
       access to the table of mounted  file  systems  for  the  current  host.
       /etc/mnttab  is read by programs using the routines described in getmn‐
       tent(3C). Mounting a file system adds an entry to this table.  Unmount‐
       ing  removes  an entry from this table. Remounting a file system causes
       the information in the mounted file  system  table  to  be  updated  to
       reflect  any  changes  caused by the remount. The list is maintained by
       the kernel in order of mount time. That is, the first mounted file sys‐
       tem  is  first in the list and the most recently mounted file system is
       last. When mounted on a mount point the file system appears as a  regu‐
       lar file containing the current mnttab information.


       Each entry is a line of fields separated by TABs in the form:

         special   mount_point   fstype   options   time



       where:

       special        The name of the resource that has been mounted.


       mount_point    The pathname of the directory on which the filesystem is
                      mounted.


       fstype         The file system type of the mounted file system.


       options        The mount options. See respective mount file system  man
                      page in the See Also section below.


       time           The time at which the file system was mounted.



       Examples  of  entries  for  the special field include the pathname of a
       block-special device, the name of a remote file system in the  form  of
       host:pathname,  or  the  name  of a swap file, for example, a file made
       with mkfile(1M).

IOCTLS
       The following ioctl(2) calls are supported:

       MNTIOC_NMNTS         Returns the count of mounted resources in the cur‐
                            rent snapshot in the uint32_t pointed to by arg.


       MNTIOC_GETDEVLIST    Returns  an  array  of uint32_t's that is twice as
                            long as the length returned by MNTIOC_NMNTS.  Each
                            pair of numbers is the major and minor device num‐
                            ber for the file system at the corresponding  line
                            in the current /etc/mnttab snapshot. arg points to
                            the memory buffer to  receive  the  device  number
                            information.


       MNTIOC_SETTAG        Sets  a  tag  word  into  the  options  list for a
                            mounted file system. A tag is a notation that will
                            appear  in  the  options  string of a mounted file
                            system but it is not recognized or interpreted  by
                            the  file  system  code. arg points to a filled in
                            mnttagdesc structure, as shown  in  the  following
                            example:

                              uint_t  mtd_major;  /* major number for mounted fs */
                              uint_t  mtd_minor;  /* minor number for mounted fs */
                              char    *mtd_mntpt; /* mount point of file system */
                              char    *mtd_tag;   /* tag to set/clear */

                            If the tag already exists then it is marked as set
                            but  not   re-added.   Tags   can   be   at   most
                            MAX_MNTOPT_TAG long.

                            Use  of this ioctl is restricted to processes with
                            the {PRIV_SYS_MOUNT} privilege.


       MNTIOC_CLRTAG        Marks a tag in the options list for a mounted file
                            system  as  not set. arg points to the same struc‐
                            ture as MNTIOC_SETTAG, which identifies  the  file
                            system and tag to be cleared.

                            Use  of this ioctl is restricted to processes with
                            the {PRIV_SYS_MOUNT} privilege.


ERRORS
       EFAULT          The arg pointer in an MNTIOC_ ioctl call pointed to  an
                       inaccessible  memory location or a character pointer in
                       a mnttagdesc structure pointed to an inaccessible  mem‐
                       ory location.


       EINVAL          The  tag  specified  in  a  MNTIOC_SETTAG  call already
                       exists as a file system option, or the tag specified in
                       a MNTIOC_CLRTAG call does not exist.


       ENAMETOOLONG    The  tag  specified in a MNTIOC_SETTAG call is too long
                       or the tag would make the total length  of  the  option
                       string for the mounted file system too long.


       EPERM           The  calling  process  does  not  have {PRIV_SYS_MOUNT}
                       privilege and either a MNTIOC_SETTAG  or  MNTIOC_CLRTAG
                       call was made.


FILES
       /etc/mnttab                 Usual mount point for mnttab file system


       /usr/include/sys/mntio.h    Header file that contains IOCTL definitions


SEE ALSO
       mkfile(1M),      mount_hsfs(1M),     mount_nfs(1M),     mount_pcfs(1M),
       mount_ufs(1M), mount(1M), ioctl(2), read(2), poll(2),  stat(2),  getmn‐
       tent(3C)

WARNINGS
       The  mnttab  file  system  provides the previously undocumented dev=xxx
       option in the option string for each mounted file system. This is  pro‐
       vided for legacy applications that might have been using the dev=infor‐
       mation option.


       Using dev=option in applications is strongly  discouraged.  The  device
       number  string  represents a 32-bit quantity and might not contain cor‐
       rect information in 64-bit environments.


       Applications requiring device number information for mounted file  sys‐
       tems  should  use the getextmntent(3C) interface, which functions prop‐
       erly in either 32- or 64-bit environments.

NOTES
       The snapshot of the mnttab information is taken any time a  read(2)  is
       performed at offset 0 (the beginning) of the mnttab file. The file mod‐
       ification time returned by stat(2) for the mnttab file is the  time  of
       the  last  change  to mounted file system information. A poll(2) system
       call requesting a POLLRDBAND event can be used to block  and  wait  for
       the  system's  mounted file system information to be different from the
       most recent snapshot since the mnttab file was opened.



SunOS 5.11                        13 Sep 2010                        mnttab(4)
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